1. Field of the Invention
The present invention concerns a hydraulic system having at least one hydraulic valve for controlling a transmission, in particular a continuously variable transmission, wherein the hydraulic valve can be controlled by a pilot circuit having at least one control element having a variable flow resistance and one control element having a constant flow resistance.
2. Description of the Related Art
A hydraulic system of that sort is adequately known from motor vehicle technology. Preferably, the hydraulic system can be used to control the control components of a continuously variable transmission, which is also called a CVT transmission.
For example, with the known hydraulic system a control element having a constant flow resistance and a control element having a variable flow resistance are used in the pilot circuit. The pilot circuit is pressurized by a supply source with a predetermined supply pressure. The supply pressure acts first on the control element having a constant flow resistance, with the control element having a variable flow resistance being connected in series with the control element having a constant flow resistance in the flow direction. The two flow resistances of the control elements thereby form a pressure divider. A control pressure conduit is connected to the connecting conduit between the control element having a constant flow resistance and the control element having a variable flow resistance, which pressurizes the hydraulic valve with a desired control pressure.
When controlling the CVT transmission, control elements with rising characteristic curves are usually used. For a variety of reasons, such as safety aspects, for example, it can be simpler and can create fewer complications if a control element having a falling characteristic curve is installed in the hydraulic system. That results in the disadvantage that it is not possible to employ the usual components, namely control elements having rising characteristic curves.
An object of the present invention is to provide a hydraulic system of the type described above, in which a falling characteristic curve is implemented and without a control element having a falling characteristic curve being utilized.